Redox Reactions of Superoxotitanium(IV) in Acidic Perchlorate Solution

摘要

The ultraviolet absorption spectrum of superoxotitanium(IV), prepared by the rapid reaction of cerium(IV) and excess peroxotitanium(IV), titanium dioxide, was determined. On the basis of extensive stopped-flow studies of the decay of superoxotitanium(IV), two forms of the complex formulated as TiO23+ and TiO2(OH)2+ are proposed. A value of 1.6/M at an ionic strength of 1.0 M (LiC1O4) was determined for the hydrolysis constant of TiO23+. The decay constant for TiO23+ (kd1) is larger than that for TiO2(OH)2+ (kd2); at 25 C, the ratio kd1/kd2 approx. 13. The redox reactions of superoxotitanium(IV) with a number of substrates were investigated by means of the multimixing, stopped-flow technique. On the basis of the variation of the second-order rate constants with (H+), it is concluded that TiO23+ is the more reactive form of superotitanium(IV) toward the anionic or neutral reductants sulfur(IV), hexachloroiridate(III), iodide ion, and bromide ion. The hydrolyzed form TiO2(OH)2+ shows increased reactivity toward the catonic reductants iron(II), titanium(III), and oxovanadium(IV). It is proposed that reduction of superoxotitanium(IV) proceeds by a 1-equiv mechanism and is a facile process; the rate constants are only slightly less than that observed for protonated superoxide, HO2.